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Some pulsars lose their steady beat

New discoveries hint at hidden population of neutron stars

IRREGULAR PULSARS Two pulsars discovered by the Arecibo Observatory (shown) spend most of their time not pulsing, suggesting a large population of undiscovered pulsars in the Milky Way.

Arecibo Observatory/NAIC/NSF

GRAPEVINE, TEXAS — A pair of cosmic radio beacons known as pulsars keep switching off and on, suggesting that there might be vast numbers of undiscovered pulsars hiding in our galaxy.

Pulsars are rapidly spinning neutron stars, the ultradense cores left behind after massive stars explode. Neutron stars are like lighthouses, sweeping a beam of radio waves around the sky. Astronomers see them as steady pulses of radio energy.

But at least two in the Milky Way seem to spend most of their time turned off, Victoria Kaspi, an astrophysicist at McGill University in Montreal, reported January 4 at a meeting of the American Astronomical Society. One, first detected at Arecibo Observatory in Puerto Rico in November 2011, only pulses about 30 percent of the time. Another, also discovered at Arecibo, laid down a steady beat just 0.8 percent of the time when observed in 2013 and 2015. Then starting in August 2015,

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